In recent years, the demand for a treatment of crude (hereinafter, corrosive crude) containing a comparatively large content of corrosive material, which had been ignored, has grown due to increasing demand for crude, sudden price jumps, and plateauing production. Meanwhile, there is a case in which it is largely difficult to treat the corrosive crude due to the deterioration of the crude distillation unit (hereinafter, referred to as a CDU) for treating crude.
The content of, for example, a corrosive material such as naphthenic acid contained in the corrosive crude is obtained by using a total acid number (hereinafter, referred to as a TAN) as an index which is the amount of potassium hydroxide (mg-KOH/g) required for neutralizing, for example, 1 g of crude, and it is evaluated that the crude has high corrosiveness as the TAN value increases. In the case of treating the crude having a high corrosiveness, since pipes or equipments are easily corroded particularly in regions in contact with the corrosive crude heated to a high temperature, it is necessary to use, for example, expensive materials such as stainless steel grade/type 317 having high corrosion resistance.
However, in the crude distillation unit, since the unit in contact with the heated corrosive crude corresponds to a preheating heat exchanger group, a heating furnace, a distillation tower, and the like in a wide range, for example, even when the existing crude distillation unit is revamped to treat corrosive crude, the revamping construction is large scale and expensive. In addition, since the period during which the crude distillation unit is stopped for the revamping construction is long, it is not possible to treat any crude during the period, and hence the opportunity loss are huge.
For some time, the corrosive crude has been treated without revamping the crude distillation unit by diluting the corrosive crude with other crude. However, in this case, there are problems in that a large amount of dilution crude is required, and the amount of the corrosive crude treated is largely limited.
Here, for example, a technology has been examined which treats the corrosive crude without revamping the existing crude distillation unit in such a manner that the TAN of the corrosive crude is decreased by neutralizing the corrosive material using a chemical (for example, PTL 1). However, there is a small number of records in which the treatment using the chemical is applied to an actual unit, and in many cases, it is not clear if the device can suppress corrosion of the device.
In addition, in PTL 2, there is disclosed a technology in which crude containing a corrosive material such as naphthenic acid is heated while in contact with inert gas in a thermal reactor so as to decompose the naphthenic acid, and the corresponding crude is separated into a volatile liquid containing naphthenic acid which is not completely decomposed and nonvolatile reactor oil having a small content of naphthenic acid. The volatile liquid neutralizes and divides naphthenic acid contained in the liquid using, for example, a basic chemical such as calcium hydroxide, and the result is mixed with the above-described nonvolatile reactor oil, thereby obtaining raw oil having a small content of naphthenic acid.
However, in the technology disclosed in PTL 2, a heat source for heating the raw oil, inert gas, a chemical for neutralizing the naphthenic acid, and the like are all required, and the variable costs required for the treatment of the raw oil are high. In addition, since the chemical is used to neutralize the naphthenic acid in the volatile liquid, as in the technology disclosed in PTL 1, even when the raw oil having a small content of naphthenic acid and obtained by adopting the technology is made to circulate in the crude treatment unit, there is a small number of proof data for determining whether corrosion of the unit has been prevented.